Methyl bonding to Fe and Fe(CO) n: : reactions of Fe − and Fe(CO) n− with methyl halides

Abstract

Rate constants for atomic iron anion and successively ligated anions Fe(CO) n − (n = 0–4) reacting with CH 3X (X = F, Cl, Br, I) were measured using a selected-ion flow tube apparatus. The results indicate that X − formation occurs as the dominant channel when exothermic. Other observed reaction channels are ligand exchange (with CH 3 and X replacing two CO), halogen-atom abstraction and adduct formation. Fe(CO) 4 − is too stable for a reaction with CH 3X to develop by any channel. Fe(CO) 2 − displays a rich chemistry. Information on the bond strengths, D[Fe(CO) n CH 3], is deduced from the results. Under the assumption that the X − product channel is observed if exothermic, we calculate the homolytic iron–methyl bond energies 0.13 eV ≤ D[FeCH 3] ≤ 1.76 eV, D[Fe(CO)CH 3] = 1.2 ± 0.2 eV, D[Fe(CO) 2CH 3] = 1.3 ± 0.3 eV, D[Fe(CO) 3CH 3] < 1.4 eV, and D[Fe(CO) 4CH 3] < 2.1 eV.